This invention relates to equipment design and more particularly to a method of mounting an optical or electrical package, such as a Butterfly package, on a substrate such as a printed circuit board.
As the demand for data bandwidth in communication systems increases, equipment designers and engineers must find ways of increasing the packaging density of the printed circuit boards (PCBs) to achieve more data bandwidth in less space at lower cost. The Butterfly package is a telecommunications industry standard package for lasers, photodiodes, power detectors, etc. The typical method of mounting a butterfly package requires machining a rectangular hole in the Printed Circuit Board (PCB), mounting or attacking the Butterfly package on the PCB, soldering the leads to the edge-launched pads, and mounting any required heatsinks on the secondary side of the PCB. The standard mounting method of a Butterfly package is problematic in several ways:
A machined or punched cut-out increases the manufacturing cost of the PCB and reduces the available PCB space for routing signal lines and placing components.
Typically, there is more volume available for heatsinks on the primary side of the PCB than on the secondary side. Increasing volume on the secondary side will necessitate increasing the inter-card spacing in a system and, consequently, reduce the overall system density.
The typical horizontal mounting of the Butterfly package, i.e. with leads extending parallel to the plane of the PCB, takes up significant board area. This standard mounting orientation reduces the PCB density and therefore the system density.
In a Butterfly package for an optical application the optical fiber associated with optical components in the package is inherently fragile. The transmission characteristics of an optical signal carried by the fiber can be changed or damaged by what is known as xe2x80x9coverbendingxe2x80x9d, i.e. bending a fiber in too small of a radius. For most Butterfly packages, the optical fiber is either in the same plane, or very close to being in the same plane as the leads extending from the package. For Butterfly packages mounted using a cut-out, as described above, an extension of the cut-out is usually necessary to allow the fiber to be routed without overbending it. This extension of the cut-out further reduces the PCB packaging density.
An alternate method of mounting the Butterfly package involves placing the package on the primary side of the board and forming or bending the leads so that they are mounted on a surface mount pad or project through and are attached to holes in the board. The long lead length required to form the leads at 90 degrees increases the series inductance of the leads so much that the component becomes unusable at high frequencies.
While Butterfly packages are typically used for packaging optical components they can also be used to package electronic circuitry. Mounting a Butterfly package will involve many of the same problems listed above regardless of what the package itself is housing. The invention is not limited to the mounting of Butterfly packages housing optical components, but includes Butterfly packages housing an electronic circuit or electro-optical circuits.
The invention concerns a novel method of mounting a Butterfly package on a PCB. Rather than mounting the package in the standard method, requiring a cut-out in the PCB, low component density, and secondary side mounted heatsinks, the invention introduces a mounting technique wherein the Butterfly package is positioned on its side. This side mounting eliminates the need for a PCB cut-out, allows for a primary side mounted heatsink, and increases the PCB density and volumetric packaging efficiency.
The connections on the now xe2x80x9cbottom sidexe2x80x9d of the Butterfly package are made as through holes in the PCB, while the leads at the now xe2x80x9ctop sidexe2x80x9d of the package are connected to the PCB via a flex circuit or ribbon connection. Depending on the application, the connections to the through-hole can be designed to support DC currents or high frequency signals. Similarly the flex circuit can be specifically designed to carry anything from DC currents to high frequency signals.
Therefore, in accordance with the present invention there is provide a method of mounting a package to a printed circuit board (PCB), the package having a body with a plurality of leads extending outwardly from opposed first and second sides of the body, the method comprising: locating the package on the PCB such that leads on the first side of the body are facing the PCB; connecting the leads on the first side to connection points on the PCB; and connecting the leads on the second side of the body to a flexible ribbon connector.